US6471724B2 - Methods and instruments for interbody fusion - Google Patents

Abstract

A laparoscopic surgical technique is provided for preparing a site for implantation of a novel fusion device or implant. In accordance with one embodiment of the technique, a laparoscope is provided having an outer sleeve with distraction fingers at one end to distract the disc space. The laparoscope provides a sealed working channel to the disc space, through which the disc space is distracted, the vertebral endplates and surrounding disc is reamed, and the fusion device inserted. A distraction plug is provided for centering the outer sleeve and for providing midline distraction of the disc space. In one embodiment, a fusion device includes diverging bone screws passing through an end wall and upper and lower walls of the device to engage the adjacent vertebrae. In another embodiment, a connector plate is engaged to bilaterally position fusion devices to prevent rotation and resist expulsion of the devices from the disc space.

Description

REFERENCE TO RELATED APPLICATIONS

This is a divisional application of co-pending U.S. patent application Ser. No. 09/014,901 filed Jan. 28, 1998, now U.S. Pat. No. 6,206,922 which is a continuation-in-part of U.S. patent application Ser. No. 08/604,874, filed Feb. 22, 1996, now abandoned which is a continuation-in-part of U.S. patent application Ser. No. 08/411,017, filed Mar. 27, 1995, now U.S. Pat. No. 5,782,919 all owned by the assignee of the present application.

BACKGROUND OF THE INVENTION

The present invention relates to methods and instruments for performing an interbody fusion of a disc space between two adjacent vertebrae. Specifically, the invention concerns laparoscopic techniques and instruments to prepare a fusion site and to insert fusion devices and implants.

The number of spinal surgeries to correct the causes of low back pain has steadily increased over the last several years. Most often, low back pain originates from damage or defects in the spinal disc between adjacent vertebrae. The disc can be herniated or can be suffering from a variety of degenerative conditions, so that in either case the anatomical function of the spinal disc is disrupted. The most prevalent surgical treatment for these types of conditions has been to fuse the two vertebrae surrounding the affected disc. In most cases, the entire disc will be removed, except for the annulus, by way of a discectomy procedure. Since the damaged disc material has been removed, something must be positioned within the intradiscal space, otherwise the space may collapse resulting in damage to the nerves extending along the spinal column.

The intradiscal space is often filled with bone or a bone substitute in order to prevent disc space collapse and to promote fusion of the two adjacent vertebrae. In early techniques, bone material was simply disposed between the adjacent vertebrae, typically at the posterior aspect of the vertebrae, and the spine column was stabilized by way of a plate or a rod spanning the affected vertebrae. Once fusion occurred the hardware used to maintain the stability of the segment became superfluous. Moreover, the surgical procedures necessary to implant a rod or plate to stabilize the level during fusion were frequently lengthy and involved.

It was therefore determined that a more optimal solution to the stabilization of an excised disc space is to fuse the vertebrae between their respective end plates, preferably with the need for anterior or posterior plating. There have been an extensive number of attempts to develop an acceptable intradiscal implant that could be used to replace a damaged disc and maintain the stability of the disc interspace between the adjacent vertebrae, at least until complete arthrodesis is achieved. These “interbody fusion devices” have taken many forms. For example, one of the more prevalent designs takes the form of a cylindrical implant. These types of implants are represented by the patents to Bagby, U.S. Pat. No. 4,501,269; Brantigan, U.S. Pat. No. 4,878,915; Ray, U.S. Pat. Nos. 4,961,740 and 5,055,104; and Michelson, U.S. Pat. No. 5,015,247. In these cylindrical implants, the exterior portion of the cylinder can be threaded to facilitate insertion of the interbody fusion device, as represented by the Ray, Brantigan and Michelson patents. In the alternative, some of the fusion implants are designed to be pounded into the intradiscal space and the vertebral end plates. These types of devices are represented by the patents to Brantigan, U.S. Pat. Nos. 4,743,256; 4,834,757 and 5,192,327.

Interbody fusion devices can be generally divided into two basic categories, namely solid implants and implants that are designed to permit bone ingrowth. Solid implants are represented by U.S. Pat. Nos. 4,878,915; 4,743,256; 4,349,921 and 4,714,469. The remaining patents discussed above include some aspect that permits bone to grow across the implant. It has been found that devices that promote natural bone ingrowth achieve a more rapid and stable arthrodesis. The device depicted in the Michelson patent is representative of this type of hollow implant which is typically filled with autologous bone prior to insertion into the intradiscal space. This implant includes a plurality of circular apertures which communicate with the hollow interior of the implant, thereby providing a path for tissue growth between the vertebral end plates and the bone or bone substitute within the implant. In preparing the intradiscal space, the end plates are preferably reduced to bleeding bone to facilitate this tissue ingrowth. During fusion, the metal structure provided by the Michelson implant helps maintain the patency and stability of the motion segment to be fused. In addition, once arthrodesis occurs, the implant itself serves as a sort of anchor for the solid bony mass.

Another interbody fusion device that is designed to permit bone ingrowth is shown in FIG.1. This device is described and claimed in co-pending parent application Ser. No. 08/411, 017, filed on Mar. 27, 1995, which disclosure is incorporated herein by reference. In one embodiment, this invention contemplates a hollow threadedinterbody fusion device10 configured to restore the normal angular relation between adjacent vertebrae. In particular, thedevice10 as shown in FIG. 1 includes anelongated body11, tapered along substantially its entire length, defining ahollow interior15 and having a largest outer diameter at theanterior end12 of the device to receive the bone growth material. Thebody11 includes anouter surface16 with opposite tapered cylindrical portions and a pair of opposite flattapered side surfaces22 between the cylindrical portions. Thus, at an end view, the fusion device gives the appearance of a cylindrical body in which the sides of the body have been truncated along a chord of the body's diameter.

The cylindrical portions includethreads18 for controlled insertion and engagement into the end plates of the adjacent vertebrae. A startedthread19 is provided at theposterior end13 of thedevice10 to facilitate engagement within a prepared bore. The outer surface of this fusion device is tapered along its length at an angle corresponding, in one embodiment, to the normal lordotic angle of the lower lumbar vertebrae. The outer surface is also provided with a number ofvascularization openings24,25 defined in the flat side surfaces, and a pair of opposite elongatedbone ingrowth slots27 defined in the cylindrical portions.

Various surgical methods have been devised for the implantation of fusion devices into a subject disc space. A patent to Dr. Gary Michelson, U.S. Pat. No. 5,484,437, discloses one such technique and the associated instruments. As described in more detail in that patent, the surgical technique involved the use of a hollow sleeve having teeth at one end that are driven into the adjacent vertebrae. These teeth and the sleeve maintain the disc space height during the subsequent steps of the procedure. In accordance with one aspect of the invention in the ‘437 patent, a drill is passed through the hollow sleeve to remove the disc and bone material to produce a prepared bore for the fusion device. The drill is then removed from the sleeve and the fusion device is positioned within the disc space using an insertion tool.

In another aspect of the procedure and instruments disclosed in the ‘437 patent, a long distractor is provided having penetrating portions that urge the vertebral bodies apart to facilitate the introduction of the necessary instruments. The long distractor can act as a guide for drilling and reaming tools concentrically advanced over the outside of the distractor to prepare the site for the fusion device.

While the Michelson technique represents a significant advance over prior surgical procedures for the preparation and insertion of fusion devices, the need for improvement remains. In particular, procedures and instruments that preserve the integrity of the surgical site are desirable. The present invention is directed to this need in the field.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, a novel fusion device is provided that integrates a pair of bone screws. The fusion device can be a hollow substantially cylindrical body, such as the device shown in FIG.1. In this aspect, the device includes a pair of screw bores formed in an end face of the body. The bores are arranged so that bone screws extending through the bores will be driven into the endplates of the adjacent vertebrae. In certain features, the heads of the bone screws are recessed within the body and held in place by a connon locking screw. The screws help prevent retrograde expulsion or rotation of the fusion device, or a spacer, from the disc space.

The present invention also contemplates another approach to preventing rotation and/or dislodgment of fusion devices placed bilaterally in the disc space. In one embodiment, a transverse connector plate is engaged by locking screws to the end walls of the bilateral fusion devices. In one feature, the end walls defme central recesses and transverse grooves to receive the connector plate. In another embodiment, the connector plate can include screw bores to receive bone screws driven into the vertebrae at a location in between the fusion devices.

In another aspect of the invention, a method is provided for preparing a subject disc space for implantation of a fusion device or implant between adjacent vertebrae. In this technique, a laparoscope is provided that includes an outer sleeve with opposite extensions at one end of the outer sleeve and a laparoscopic port engaged at the outer end of the outer sleeve, the laparoscopic port having a number of seals, with the opposite extensions configured to maintain distraction of the adjacent vertebrae.

The preferred technique comprises the steps of making an incision in the skin of the patient aligned with the subject disc space, retracting tissue beneath the incision to expose the disc annulus; and piercing the disc annulus to create an opening. The outer sleeve of the laparoscope is advanced through the incision, leaving the port outside the skin of the patient while inserting the opposite extensions into the disc space with the outer sleeve contacting the disc annulus. The laparoscope, and particularly, the outer sleeve, creates a protected working channel between the disc space and the laparoscopic port outside the patient.

In a further step of the preferred inventive technique, a reamer is operated through the number of seals and the outer sleeve of the laparoscope to create a prepared bore in the disc material and the adjacent vertebrae for implantation of a device into the bore.

In a most preferred embodiment of the surgical technique, the technique comprises the steps of percutaneously exposing the annulus of the disc in the subject disc space through an incision in the skin of the patient and piercing the disc annulus to create an opening. A distractor can then be inserted through the incision and through the opening into the disc space to distract the vertebrae adjacent the subject disc space. The laparoscope outer sleeve is then introduced through the incision and over the distractor, leaving the port outside the skin of the patient while inserting the opposite extensions through the opening into the disc space to create the protected working channel between the port and the distractor tip.

In subsequent steps, the distractor is removed and a reamer is advanced through the number of seals of the laparoscope and through the outer sleeve into the disc space to ream the disc space and adjacent vertebrae to create a prepared bore for the fusion implant. After the reamer is removed from the laparoscope, the fusion implant can be advanced through the number of seals and through the outer sleeve into the prepared bore. With the fusion implant in position, the laparoscope can be withdrawn from the patient.

In one aspect of the invention, a switching sleeve is placed within the outer sleeve of the laparoscope with an end of the switching sleeve projecting beyond the opposite fingers of the outer sleeve, the end of the switching sleeve being tapered to minimize trauma to tissue adjacent the subject disc space as the outer sleeve adjacent into the patient with the switching sleeve projecting beyond the opposite extensions of the outer sleeve.

In a further embodiment, the laparoscopic method is used for bilateral placement of two fusion devices into a subject disc space. In addition to the steps previously described, this embodiment of the surgical technique includes unseating the outer sleeve of the laparoscope from the first opening in the disc annulus by withdrawing the laparoscope until the opposite extensions of the outer sleeve are outside the disc annulus. With the switching sleeve in position within the outer sleeve, the laparoscope is moved to the second opening in the disc space without removing the laparoscope from the patient. The steps for preparing the bore to receive a fusion implant can be repeated. In one specific embodiment, these steps are conducted at the second opening with the distractor remaining within the first opening. After a fusion implant is advanced through the number of seals and through the outer sleeve into the second prepared bores the laparoscope can then be returned to the first opening for insertion of another fusion implant. During this step, the fusion implant contained within the second prepared bore maintains distraction of the disc space.

As an adjunct to this inventive technique, a distraction device is provided in one aspect of the invention. The distraction device can include an elongated stem sized for insertion along the A-P midline of the intervertebral disc space. Preferably, opposite surfaces of the device include a number of ridges that operate as bone engaging surfaces to resist expulsion of the device. In one important feature, the stem of the distraction device includes a bore to receive a spike projecting from a tubular body, such as the outer sleeve discussed above. With this feature, the distraction device acts not only as a midline distractor, but also as a centering guide to locate the tubular body through which subsequent surgical procedures can be performed.

In a further feature, the distraction device can include a flange projecting from the stem. The flange has a bone contacting that transmits to the vertebra a force applied to the distraction device (preferably by a manual tool). This flange can be used to reduce a high grade spondylolisthesis condition as the distraction device is driven into the disc space.

One object of the present invention is to provide surgical technique and instruments that permit the preparation of a disc space for insertion of a fusion implant under a sealed condition. A further object of the invention is to implement laparoscopic techniques to implant fusion devices.

With respect to fusion devices, one object is to enhance the stability of the device in situ while reducing the risk of expulsion of the device. Yet another object is to provide means for readily reducing a spondylolisthesis condition from a laparoscopic approach.

One benefit of the present invention is that all of the steps necessary to prepare a disc space and to implant a fusion device can be conducted in a protected environment. In addition, the inventive techniques and instruments allow minimal intrusion into the patient, which minimized the risks normally associated with spinal surgery.

Other objects and benefits can be discerned from the following written description and accompanying figures.

DESCRIPTION OF THE FIGURES

FIG. 1 is a side perspective view of a threaded fusion device having a tapered configuration to restore the normal angle of a spinal motion segment.

FIG. 2 is a top elevational view of an implant driver for use in engaging and driving a fusion device such as the device shown in FIG.1.

FIG. 3 is an enlarged perspective view of the end of the implant driver shown in FIG. 2 engaged to a fusion device such as shown in FIG.1.

FIG. 4 is an enlarged side cross-sectional view of the implant driver and fusion device shown in FIG.3.

FIG. 5 is an enlarged side cross-sectional view of an alternative embodiment of an implant driver for engaging and driving a fusion device such as the device shown in FIG.1.

FIG. 6 is a driving tool attachment according to one aspect of the present invention.

FIG. 7 is an enlarged side cross-sectional view similar to the view in FIG. 5 with the driving tool attachment of FIG. 6 engaged between the implant driver and the fusion device.

FIG. 8 is an end perspective view of a threaded fusion device according to a further embodiment of the invention.

FIG. 9 is a side perspective view of a driving tool attachment according to a further aspect of the present invention in which the driving tool attachment is configured to engage the fusion device depicted in FIG.8.

FIG. 10 is a side partial cross-sectional view of a fusion device according to the embodiment of FIG. 8 disposed between adjacent vertebrae and engaged in position by a pair of bone screws in accordance with one aspect of the present invention.

FIGS.11(a)-(d) are lateral representations of the spine showing four steps of a surgical method for implanting a fusion device such as the device in FIG. 1 according to an anterior approach in one aspect of the present invention.

FIGS.12(a)-(d) are lateral representations of the spine showing four steps of a surgical method for implanting a fusion device such as the device in FIG. 1 according to a posterior approach in a further aspect of the present invention.

FIG. 13 is a frontal view of a patient with locations identified for surgical incisions according to a preferred embodiment of the present inventive laparoscopic surgical technique.

FIG. 14 is an A-P representation of a spinal segment at the laparoscopic surgical site depicting one step of the inventive surgical technique in which bilateral locations are marked on the disc annulus for insertion of a pair of fusion devices, such as the device shown in FIG.1.

FIG. 15 is an enlarged A-P view of the disc at the spinal segment showing the use of the template represented in FIG. 14 of the invention.

FIG. 16 is an A-P representation of the laparoscopic surgical site depicting a further step of the inventive surgical technique of creating a pilot hole at each of the bilateral locations marked in the step shown in FIG.14.

FIG. 17 is an A-P representation of the laparoscopic surgical site depicting a further step of the inventive surgical technique of using a trephine to create a bore at each of the bilateral locations marked in the step shown in FIG.14.

FIG. 18 is an A-P representation of the laparoscopic surgical site depicting a further step of the inventive surgical technique for inserting a distractor into the prepared site at each of the bilateral locations marked in the step shown in FIG.11.

FIG. 19 is a perspective representation of the laparoscope according to the present invention in which the outer sleeve of the laparoscope is engaged within the subject disc space.

FIG.20(a) is a perspective representation of the laparoscope of FIG. 19 with a switching sleeve according to one aspect of the invention disposed within the laparoscope.

FIG.20(b) is an enlarged A-P representation of the laparoscope and switching sleeve of FIG.20(a) showing the positioning of the distractor tip as depicted in FIG.18.

FIG. 21 is a perspective representation of the laparoscope of FIG. 19 with a reamer extending through the laparoscope to prepare the site for receiving a fusion device.

FIG. 22 is a perspective view of an implant driver of the type shown in FIG. 2 engaged to a fusion device and including a T-handle assembly engaged to the driver.

FIG. 23 is a perspective view of an implant holder according to one aspect of the present invention.

FIG. 24 is a perspective representation of the laparoscope used to implant a bone dowel within the prepared site and including a bone dowel impactor in accordance with one aspect of the present invention.

FIG. 25 is a top perspective view of a distraction plug in accordance with one embodiment of the present invention.

FIG. 26 is a side cross-sectional view of the distraction plug shown in FIG.25.

FIG. 27 is an end elevational view of the distraction plug shown in FIGS. 25 and 26.

FIG. 28 is a side view of the distraction plug shown in FIG. 25 as it is inserted between adjacent vertebrae using a plug driver in accordance with one aspect of the present invention.

FIG. 29 is a side perspective view of a distraction plug in accordance with a further embodiment of the present invention.

FIG. 30 is a side perspective view of a plug driver in accordance with a further embodiment of the invention configured for engaging a distractor plug as shown in FIG.29.

FIG. 31 is a rear perspective view of a percutaneous surgical sleeve in engagement with a distractor plug in accordance with the embodiment shown in FIG.25.

FIG. 32 is a superior A-P view of a vertebra of the spine with the distractor plug and percutaneous surgical sleeve shown in FIG. 31 disposed within the disc space, with an alternative position of the sleeve shown in phantom.

FIG. 33 is a side perspective view of a percutaneous surgical sleeve in accordance with a further embodiment of the invention with an outrigger spike engaged thereto for attachment to a distractor plug according to FIGS. 25 or29.

FIG. 34 is an end perspective view of a double barrel percutaneous surgical sleeve configured for engaging a distractor plug, such as the distractor plug shown in FIG.29.

FIG. 35 is a side perspective view of an assembly in accordance with a further embodiment of the present invention utilizing a pair of fusion devices connected by a connector plate.

FIG. 36 is a side perspective view of an alternative embodiment of the assembly with a pair of fusion devices interconnected by an alternative connector plate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

As described above, one interbody fusion device, as shown in FIG. 1, can be implanted within the intradiscal space. Thisinterbody fusion device10 can be implanted using theimplant driver50 shown in FIG.2. Theimplant driver50 is comprised of ashaft51 andsleeve52 concentrically disposed about the shaft.Tongs54 are formed at one end of the shaft for gripping theinterbody fusion device10 for implantation. Preferably the tongs include a taperedouter surface55 and an opposite flatinner surface56 adapted to engage thetruncated side walls22 of the interbody fusion device as shown in FIGS. 3,4. Most preferably the taperedouter surface55 conforms to the root diameter of the interruptedthreads18 of thedevice10 so that thetongs54 essentially complete the full cylindrical shape of thebody wall16. The adaptation of the tongs' taperedouter surface55 facilitates screw insertion of theinterbody fusion device10 since theouter surface55 will ride within the tapped bore in the vertebral end plates.

Each of thetongs54 can be provided with interlockingfingers58 and a drivingprojection59 extending from theinner surface56, most clearly shown in FIG.4. Referring again to FIG. 2, theshaft51 defines ahinge slot62 supporting each of the pair oftongs54. Thehinge slot62 is configured so that the tongs will have a naturally biased position spread sufficiently apart to accept thefusion device10 therebetween. Theshaft51 defines aconical taper63 between the hingedslot62 and each of thetongs54. This conical taper mates with aconical chamfer67 defined on the inner wall of thesleeve52. Thus, as thesleeve52 is advanced toward thetongs54, theconical chamfer67 rides against theconical taper63 to close or compress thehinge slot62. In this manner, thetongs54 are pushed toward each other and pressed into gripping engagement with the interbody fusion device situated between the tongs.

Theshaft51 andsleeve52 are provided with a threadedinterface65 which permits thesleeve52 to be threaded up and down the length of the shaft. Specifically, the threadedinterface65 includes external threads on theshaft51 and internal threads on thesleeve52 having the same pitch so that the sleeve can be readily moved up and down theimplant driver50. Theshaft51 is also provided with a pair ofstops69 which restrict the backward movement of thesleeve52 to only the extent necessary to allow thetongs54 to separate a sufficient distance to accept theinterbody fusion device10.

The use of theimplant driver50 is shown with reference to FIGS. 3,4. As can be seen in FIG. 3, theouter surface55 of thetongs54 reside generally flush with the root diameter of the interruptedthreads18. As seen in FIG. 4, the interlockingfingers58 can be arranged to fit within thevascularization opening24 on each of thetruncated side walls22. In a similar fashion, the drivingprojections59 engage thedriving tool slots29 at theanterior end12 of theconical body11. The combination of the interlockingfingers58 and drivingprojections59 firmly engage theinterbody fusion device10 so that the device can be screw threaded into a tapped or untapped opening in the vertebral bone. Thetongs54 in this embodiment are configured to engage thefusion device10 and to impart a threading or rotational force to the device. It is understood that the tongs can adopt other configurations depending upon the structure of the fusion device to be implanted.

An alternative embodiment of the implant driver is shown in FIG.5. Thedriver90 includes ashaft91, having a length sufficient to reach into the intradiscal space from outside the patient. Connected to the end ofshaft91 is a head which defines a pair ofopposite tongs93, each of which are configured for flush contact with the flattruncated side walls22 of thefusion device10. Like thetongs54 of the previously describedimplant driver50, the outer surface of the tongs is cylindrical to correspond to the cylindrical threaded portion of the device.

Unlike theimplant driver50, thedriver90 of the embodiment in FIG. 5 uses an expanding collet assembly to firmly grip thefusion device10 for insertion into the body. Specifically, thehead92 adefines acollet94 having a central collet bore95 formed therethrough. Thecollet94 terminates in anannular flange96 that at least initially has a diameter slightly smaller than the inner diameter of thefusion device10 at itsend12. Anexpander shaft97 slidably extends through the collet bore and includes a flaredtip98 situated adjacent and extending just beyond theannular flange96. The flaredtip98 of theexpander shaft97 starts at a diameter sized to slide within the collet bore95 and gradually flares to a diameter larger than the bore.

Theimplant driver90 further includes apuller shaft99 slidably disposed within abore100 defined in theshaft91. Thepuller shaft99 has a lockingchamber101 at its end which engages alocking hub102 formed at the end of theexpander shaft97. Thepuller shaft99 projects beyond the end of theshaft91 for access by the surgeon. When thepuller shaft99 is pulled, it pulls theexpander shaft97 away from theannular flange96 of thecollet94 so that the flaredtip98 becomes progressively engaged within the collet bore95. As thetip98 advances further into thebore95, theannular flange96 expands from its initial diameter to a larger second diameter sufficient for firm gripping contact with the interior of thefusion device10. With the fusion device so engaged, the implant driver can be used to insert thedevice10 into the surgical site, after which the expander shaft can be advanced beyond the collet bore to release the flat tip and, consequently, the fusion device.

In certain circumstances, it may be necessary to drive thefusion device10 deeper into the disc space. When either of theimplant drivers50 or90 is engaged to the fusion device, the device can be readily advanced farther into the disc space. However, once the implant driver is removed and it is then discovered that the fusion device needs to be repositioned, the flexible nature of thetongs54 and93 of the two implant drivers makes reacquisition of the now implanted fusion device difficult. To alleviate this difficulty, adriving tool attachment120 is provided, as shown in FIG.6. Thedriving tool attachment120 includes abody121 having afirst end122 and an oppositesecond end123. Like the fusion implant, thebody121 of thedriving tool attachment120 includes acylindrical portion125 and oppositeflat side portions126. Theopposite side portions126 are configured to be engaged by the tongs of theabove driving tools50 or90.

Thedriving tool attachment120 includes a pair of opposingflanges130 atend123. Theflanges130 are configured to engage the oppositeflat surface122 on thefusion implant10, in a manner similar to that accomplished by the tongs of theimplant driver50 and90. Theend123 also includes aboss131 which is configured to be inserted into the opening at the end of the implant10 (see FIG.7). In use, thedriving tool attachment120 can be engaged with one of thedriving tools50 or90, with the tongs firmly grasping theflat surfaces126, as shown in FIG.7. The driving tool attachment can then be advanced into the disc space with theflanges130 oriented across the space so that they can readily interface with theflat surfaces22 of thefusion device10. When thedriving tool attachment120 is properly aligned, theboss131 projects into thehollow opening15 at theanterior end12 of the fusion device and theflanges130 engage the oppositeflat surfaces22 of the device. The driving tool can then be rotated as if the fusion implant were directly engaged to the main driving tool. The attachment readily transmits the rotational driving force to theimplant10 to thread it deeper into the disc space or to retract it back within the disc space. One particular advantage provided by thedriving tool attachment120 is that the relatively flexible tongs of the twodriving tools50 and90 can be already engaged to theattachment120 before insertion into the surgical site. This eliminates a great deal of fiddle factor and avoids the risk that the tongs would be unable to firmly grasp theimplant10 when it is already in position within the disc space.

In a further embodiment of the present invention, an interbody fusion device is provided that permits supplemental fastening to the adjacent vertebrae. In particular, aninterbody fusion device250, as depicted in FIG. 8, includes ahollow body251 having afirst end252 and asecond end253. Thehollow body251 defines ahollow interior255 and includes anend wall256 at thefirst end252. Like thefusion device10 shown in FIG. 1, theinterbody fusion device250 includesexternal threads258 spanning a substantial portion of the length of thehollow body251, and acontinuous thread259 adjacent thesecond end253 of the body. Also like thefusion device10, theinterbody fusion device250 includes oppositeflat sidewalls262 that interrupt theexternal threads258, as well as opposingslots263 offset from theflat sidewalls262 which also interrupts a portion of theexternal threads258. Thus far, theinterbody fusion device250 is substantially similar to thedevice10 shown in FIG.1. For example, the device can be tapered so that it has a larger diameter at thefirst end252 than at thesecond end253. In addition, side windows264 (see FIG. 10) can be provided in theflat sidewalls262. Theside walls262 essentially divide thebody251 into upper and lower threaded portions that are configured to be threadedly driven into adjacent vertebrae.

In accordance with this embodiment, theinterbody fusion device250 includes a pair ofdriver openings265 defined in theend wall256 at thefirst end252. Intermediate between thedriver openings265 are a pair of offset screw bores267. In this preferred embodiment, the screw bores267 are formed so that their respective longitudinal axes intersect and project out from the top andbottom portions260,261. Preferably the axes are arranged to intersect theslots263 in the top and bottom of the fusion device. In this configuration, the longitudinal axes of the two screw bores intersect outside thehollow body251 and theend wall256, as seen in FIG. 10. A threadedbore270 is formed between the two screw bores267. The screw bores267 also define a recessedportion268, while the threaded bore defines a recessedportion271 that intersects each of the recessedportions268 of the screw bores267 at anoverlap272.

In using theinterbody fusion device250, adriving tool attachment275 is provided that permits insertion of the device within a properly prepared intervertebral space. As depicted in FIG. 9, thedriving tool attachment275 is similar to the implant driver shown in FIG.6. In this instance, thedriving tool attachment275 includes abody276 having oppositeflat sidewalls277, so that the body is adapted to be engaged by theimplant driver90 in the manner depicted in FIG.7. In accordance with the present embodiment, thedriving tool attachment275 includes a pair of spaced-apart drivingbosses278 projecting from amating face279. Thebosses278 are sized and shaped to fit within thedriver openings265 when themating face279 is in direct contact with theend wall256 of thefusion device250. Thedriving tool attachment275 can be engaged to a fusion device, such asdevice250, to permit threading of the device into the intervertebral disc space, such as the space between lumbar vertebrae L4 and L5, as shown in FIG.10.

With thefusion device250 appropriate positioned within the intervertebral disc space, a pair of bone screws280 can be extended through respective screw bores267 in thehollow body251. The screws are passed through thebores267 until the bone engaging threads of thescrews280 contact the vertebral bone. As the bone screws280 are threaded into the vertebral bone, thehead281 of each of the bone screws280 seats within the respective recessedportions268 of each of the screw bores267. In this orientation, theheads281 of the bone screws280 are flush with or below the surface of theend wall256 of thefusion device250. At this point, a lockingscrew282 can be threaded into the threadedbore270. As the locking screw is tightened into thebore270, thehead283 of the locking screw contacts theheads281 of both bone screws280. Further tightening of the lockingscrew282 causes thehead283 to seat within the recessedportion271 to trap theheads281 of the bone screws280 within their respective screw bores267. Thus, theset screw282 prevents backout of the bone screws280 when they are engaged within the adjacent vertebrae.

The diverging bone screws280 provide greater stability to thefusion device250 than can be achieved with prior threaded devices. The bone screws enhance the resistance to retrograde expulsion of the device and prevents counter-rotation or unthreading. The bone screws280 can be of a wide range of sized provided that the screws are long enough to achieve an effective purchase in the adjacent vertebrae.

In accordance with additional aspects of the present invention, two methods for implanting an interbody fusion device, such as thedevices10 or250, are contemplated. First, with reference to FIGS.11(a)-11(d), an anterior approach is shown. As a preliminary step, it is necessary to locate appropriate starting points for implanting the fusion device, preferably bilaterally. In the first step of the anterior approach, adistractor75 is disposed between the vertebral end plates E to dilate the L4-L5 or L5-S1 disc space. (It is understood, of course, that this procedure can be applied at other vertebral levels). In the second step, shown in FIG.11(b), anouter sleeve76 is disposed about the disc space. Theouter sleeve76 can be configured to positively engage the anterior aspect of the vertebral bodies to firmly, but temporarily, anchor theouter sleeve76 in position. In essence, thisouter sleeve76 operates as a working channel for this approach. In the step of FIG.11(b), adrill77 of know design is extended through the outer sleeve and used to drill out circular openings in the adjacent vertebral bodies. The openings can be tapped to facilitate screw insertion of thefusion device10, although this step is not necessary.

In the next step shown in FIG.11(c), thefusion device10 is engaged by theimplant driver50 and extended through theouter sleeve76 until thestarter thread19 contacts the bone opening. Theimplant driver50 can then be used to screw thread the fusion device into the tapped or untapped opening formed in the vertebral end plate E. It is understood that in this step, other suitable driving tools could be used, such as a screw driver configured to engage thedriving tool slots29 at theanterior end12 of thedevice10. The degree of insertion of thefusion device10 determines the amount of lordosis added or restored to the vertebral level. In the final step, the implant driver is removed leaving thefusion device10 in position. It can be seen that once implanted, the closedposterior end13 is directed toward the posterior aspect of the vertebrae. Thehollow interior15 is open at itsanterior end12, but can be closed by a plastic or metal material, if necessary.

In a second inventive method, as depicted in FIGS.12(a)-12(d), a posterior approach is implemented. The first two steps of the posterior approach are similar to that of the prior anterior approach, except that thedistractor75,outer sleeve76 anddrill77 are introduced posteriorly at the instrumented motion segment. This approach may require decortication and removal of vertebral bone to accept theouter sleeve76. In the third step of this method, thefusion device10 is inserted through theouter sleeve76 into the dilated disc space. It is understood that the disc space is preferably dilated only to the extent necessary to receive the implant with thetruncated side walls22 directly facing the vertebral end plates E. Thus, as shown in FIG.12(c), thebone ingrowth slot27 is facing laterally, rather than coronally, as expected for its final implanted position. Asuitable driving tool80 can be provided to project thefusion device10 through theouter sleeve76 and into the intradiscal space. In one embodiment, the drivingtool80 includes aprojection81 which is configured to engage a slot opening formed in the end wall at theposterior end13 of thefusion device10. An internal thread (not shown) can be used to fix thedevice10 to thedriver80.

Once thefusion device10 has been advanced into the intradiscal space to the appropriate depth relative to the pivot axis P of the vertebrae, the drivingtool80 is used to rotate the implant in the direction of the rotational arrow R in FIG.12(c). As the drivingtool80 is rotated, the device itself rotates so that the interruptedthreads18 start cutting into the vertebral bone at the end plates E. In this manner, the implant operates as a cam to separate the adjacent vertebrae in the direction of the spreading direction arrows S in FIG.12(c). This camming approach provides a somewhat easier insertion procedure than for the anterior approach of FIGS.11(a)-(d) in that a single rotation is required to lock the implant into the vertebral bone. In contrast, the formerly discussed screw insertion technique of the anterior approach requires continuous threading of the device into position.

With either the anterior (FIGS.11(a)-(d)) or the posterior approach (FIGS.12(a)-(d)), the position of thefusion device10 with respect to the adjacent vertebrae can be verified by radiograph or other suitable techniques for establishing the angular relationship between the vertebrae. Alternatively, the preferred depth of insertion of the implant can be determined in advance and measured from outside the patient as the implant is positioned between the vertebrae. The depth of insertion of the fusion device can be ascertained using depth markings (not shown) on theimplant drivers50,90 or80.

In another embodiment of the inventive surgical technique, laparoscopic technology is used to provide a sealed and protected channel for instruments and implants directed to the subject disc space. In accordance with one aspect of this inventive method, an anterior approach to the L5-S1 motion segment is illustrated. It is of course understood that these same techniques and instruments to be described below could be used at different vertebral levels or in a posterior approach under appropriate conditions.

As depicted in FIG. 13, the present inventive technique includes making asmall incision140 and preferably inserting an insufflator needle into the abdominal cavity. Fluid is introduced into the abdominal cavity through the insufflator needle to a pressure of preferably approximately1 Smm of mercury to assist in visualization of the surgical site. Aninitial port141 for the laparoscope is placed five to ten centimeters cephalad of the umbilicus in the midline ten millimeters in length. The abdomen is visually explored and the patient is placed in steep Trandelenburg. The abdominal wall is visualized endoscopically as two workingports142,143 are placed just lateral to the epigastric vessels, opposite the level or levels to be fused. It is believed to be advantageous to stagger the ports slightly from direct opposition to each other.

The preferred method continues with insertion of retractors through theports142,143. The retractors can be used to sweep the small bowel superiorly out of the pelvis. The sigmoid colon is also pulled out of the pelvis and held laterally with the left fan retractor. For fusion at the L5-S1 junction, the sacral promontory and drop-off can be easily seen at this point. The posterior peritoneum overlying the L5-S1 disc space is then incised longitudinally with endoshears for the desired exposure. Using opposing fan retractors as blunt dissectors, the soft tissue underlying the parietal peritoneum can be swept laterally to bilaterally expose the anterior L5-S2 disc annulus. The sacral artery and vein coursing the disc are individually ligated with hemoclips and transected. A dissector can be used to remove residual soft tissue over the disc. Exposure is maintained with the left fan retractor in place holding the colon out of the way. It has been found that usually the right side does not require retraction, so a suction irrigation catheter can be used through this port.

In one specific procedure for the L4-L5 disc, the posterior peritoneum is incised more proximally about3 centimeters. Again, the left fan is used to retract the colon laterally and with careful blunt dissection the aorta is exposed anteriorly at the bifurcation. The L4-L5 disc is usually right below this point. Left lateral dissection is carried out over the left common iliac vein and artery, gently retracting these vessels to the right. In order to retract these vessels enough to the right for adequate disc exposure the ascending segmental vein branch must be identified and transected. Once this vessel is cut, the artery and vein can then be bluntly retracted to the right with a fan or loop retractor to expose a significant amount of the L4-L5 disc for fusion.

Once the subject disc is exposed, it can be important to align the abdominal entry operatingtrocar port site145 with the disc to be fused so that the operating trocar is parallel with the endplates of the disc in the sagittal plane. The entry point is estimated and a small Steinmann pin can be placed either in the interspace or along the patient and checked with lateral C-arm and adjusted accordingly. A 1.5 to 2.5 centimeter incision can be made for placement of the operating trocar. A blunt introducer is placed in the abdomen and an 18 mm working trocar147 (FIG. 14) can be placed over it under endoscopic visualization.

In accordance with a further aspect of the present embodiment of the surgical technique, the annular of the subject disc D is marked for bilateral placement of a pair of fusion devices. For example, as shown in FIG. 14, a workingtrocar147 is situated within the working port145 (see FIG.13). The bilateral marks can be made with atemplate150, as shown in general in FIG.14 and in more detail in FIG.15. Greater detail concerning this template and its method of use can be found in U.S. Pat. No. 5,645,549, issued on Jul. 8, 1997. The description of this template in this co-pending application is incorporated herein by reference.

For convenience, a brief description of the template will be made with specific reference to FIG.15. In particular, thetemplate150 includestubular body151 and anelongated guide foot152 that is pivotable connected to theend153 of the tubular body. A guide wire orstylet155 extends through the tubular body to pivot thefoot152 to the side. Thesharp tip156 of the stylet can then be used to pierce the disc annulus D. Using a mallet, the template can be secured to the center of the disc space by driving thestylet156 into the disc tangential to the curvature of the annulus and parallel to the endplates. The template can then be slide down the guide wire or stylet until thefoot152 contacts the disc annulus.

The foot includes anopening157 through which anelectrocautery device160 can extend. Thetip161 of the electrocautery device is guided through theopening157 in thefoot152 to contact the disc annulus D. When thetip161 is energized, it leaves a mark MR that is lateral to the center of the subject disc. Thetemplate150 can then be rotated in the direction of the arrow T so that the foot is situated laterally opposite the first mark MR. At that point, the electrocautery device can be used to make a second mark ML providing the bilateral positions for the two fusion devices.

Once the bilateral marks MR, ML have been made on the disc annulus, the surgeon has a visual indication as to the proper location for placement of the fusion device. Under direct visualization of the insufflated abdominal region by way of a laparoscope through port141 (FIG.13), the surgeon can then direct a T-handle probe160 through the workingport147 to the either of the cauterization marks MR and ML (FIG.16). The T-handle probe160 includes asharp tip161 that is used to break through the disc annulus. The T-handle allows the surgeon to rotate theprobe160 as necessary to facilitate penetration into the annulus. Once an initial opening has been made in the disc annulus by way of theThandle probe160, a T-handle trephine165 can be used to create pilot holes for subsequent instrumentation. The T-handle trephine165 can include a series of marking166 at 5 mm increments to control the depth of insertion of the trephine into the disc space, as shown in FIG.17. Themarkings166 are compared to the workingtrocar147 to gauge the depth of the cutting edge of the trephine, and therefore the depth of the prepared bore in the disc space and vertebral endplates. Again, the T-handle of the trephine allows the surgeon to rotate thetrephine165. This procedure is repeated at both of the electrocautery marks ML and MR. At this point, the surgeon has two bilateral holes to use for orientation during the remainder of the procedure. Thetrephine165 is also preferably used to core into the disc space to form bilateral bores. A rongeur may be used to clear disc material from each of the bilateral bores in the disc.

In accordance with further steps of the present inventive method, adistractor167 is advanced through the workingtrocar147 as shown in FIG.18. The distractor has adistractor tip169 that is selected according to the vertebral level being instrumented. For instance, distractors for a 16 mm size implant can be either 12 mm or 14 mm in width to maintain the disc space at its proper anatomical height. Thetip169 is removably attached to adistractor shaft168. Preferably, progressively larger distractor tips are sequentially inserted in alternating fashion into each of the bilateral holes in the disc space and annulus until the annulus is taut and the adjacent vertebrae are adequately distracted for restoration of a proper disc space height. In one aspect of the invention, thedistractor tips169, once they are disposed in their bilateral positions, will acts as a centering point or alignment guide for use of the instruments throughout the remainder of the procedure. It is therefore important that thedistractor tips169 be properly located, which can be accurately confirmed with fluoroscopy.

Once the bilateral distractor tips have been properly seated, a shaft extension (not shown) can be engaged todistractor shaft168. At this point, in accordance with the preferred embodiment, thedisposable trocar147 is removed and alaparoscope170 is introduced through theport145 in the skin and into the disc space, using the distractor shaft and distractor tip as a positioning guide. In accordance with one embodiment of the present invention, thelaparoscope170 includes anouter sleeve171 having afirst end172 and asecond end173, as shown in FIG.19. Thesecond end173 is engaged to alaparoscopic port180 which can be of conventional design. In particular, thelaparoscopic port180 can include a bore184 (FIG.20(a)) extending therethrough and in communication with the interior of the hollowouter sleeve171. This bore184 in the laparoscopic port allows introduction of instruments through the port and into theouter sleeve171. The bore is preferably closed by a number ofseals182, which are configured to accept cylindrical tools and instruments therethrough while maintaining tight sealed engagement about the instrument.

Thelaparoscopic port180 also preferably includes atrumpet valve183, which can be of conventional design. Specifically, thetrumpet valve183 maintains thelaparoscopic port180 in a normally closed position in which its internal bore is closed from communication with theouter sleeve171. However, once a instrument is introduced into theport180 through theseals182, thetrumpet valve183 moves aside to allow passage of the instrument or tool into thesleeve171.

In a further unique aspect of the invention, theend172 of theouter sleeve171 includes a pair of opposite distraction extensions orfingers173. Thesedistraction fingers173 are sized according to the height of the particular disc space. Specifically, thefingers173 are intended to maintain the spacing between the adjacent vertebrae during subsequent steps of the procedure after thedistractor tip169 has been removed. Thus, the width of thefingers173 can be varied depending upon the particular vertebral level being instrumented. In addition, thedistraction fingers173 can be tapered to conform to a normal angle between adjacent vertebrae at the instrumented level. The position of the fingers713 is correlated with the position of the distractor tips within the bilateral bores in the disc space by aligning thefingers173 with thetrumpet valve183 when theport180 is engaged to theouter sleeve171. When thelaparoscope170 is inserted, the trumpet valves provide a visual indication of the alignment of the fingers. In other words, when thetrumpet valve183 is lateral to the midline, thefingers173 are properly oriented between the vertebral endplates.

In one specific embodiment, theouter sleeve171 can includeopposite spikes174 disposed between thedistraction fingers173. These spikes are preferably configured to penetrate at least partially into the adjacent vertebral bodies, to help maintain the position of theouter sleeve171 at the surgical site. In some instances, theouter sleeve171 does not include theteeth174. For example, where the procedure is to implant a tapered fusion device, theteeth174 are preferably eliminated and where the device is a uniform cylinder, the teeth can be retained.

In one embodiment of the present surgical method, thelaparoscope170 can be directly inserted over the distractor shaft extension (not shown). However, it is believed that thedistraction fingers173 and thespikes172 can cause trauma to the skin during entry and to the soft tissue surrounding the surgical site during introduction of thelaparoscope170. Thus, a further feature of the preferred embodiment includes a switchingsleeve190, as shown in FIGS.20(a), (b). The switchingsleeve190 has a length sufficient to span the entire length of thelaparoscope170 from the port seals182 to theend172 of theouter sleeve171. In particular, the switchingsleeve190 has a taperedtip191 configured to extend beyond theend172 of theouter sleeve171, and more particularly beyond the ends of thefingers173. The switchingsleeve190 also includes a flaredtip192 at its opposite end that is enlarged to prevent its passage through thelaparoscopic port180 and particularly theseals182. In accordance with a preferred embodiment of the inventive surgical procedure, the switchingsleeve190 is placed inside thelaparoscope170 prior to insertion into the patient. The switchingsleeve190 has an outer diameter nearly equal to the inner diameter of theouter sleeve171 to slide in close running fit within thelaparoscope170. Thelaparoscope170 and switchingsleeve190 can then be slide over the distractor shaft and with a twisting motion pass through the skin and fascia until the outer sleeve contacts the disc annulus. It is important to consider that theopposite fingers173 on theouter sleeve171 of the laparoscope must pass through the opening in the disc space and be aligned between the adjacent vertebrae. As thefingers173 are pushed into the disc space, the switchingsleeve190 will remain outside the disc annulus as its taperedtip191 contacts the annulus in the region between the distraction fingers173 (see FIG.20(b)). Theouter sleeve171 of thelaparoscope170 is properly oriented when thefingers173 are correctly oriented between and contacting the adjacent vertebra endplates. Theouter sleeve171 is then seated by striking a driving cap (not shown) mounted on the laparoscopic port, to thereby drive thefingers173 fully into the disc space between the vertebral endplates and to drive thespikes174 into the adjacent vertebrae.

With thelaparoscope170 in place, all of the remaining steps of this inventive technique occur under a relatively protected or sealed environment. Specifically, theouter sleeve171 of the laparoscope provides a sealed passageway from the bilateral bores at locations MR and ML on the disc to thelaparoscopic port180 outside the patient. Thelaparoscope170 can be used as a passageway to provide irrigation and aspiration where necessary, without the risk of fluids leaking into the space adjacent the operative site. Moreover, the sealed working channel to the prepared sites in the disc space prevent leakage of abdominal distension fluids into the working channel and disc space. This latter aspect allows direct vision of the surgical site outside the working channel created by the laparoscope.

With thelaparoscope170 in position, thedistractor shaft168 is removed as well as thedistractor tip169 that is disposed between the adjacent vertebrae. Since thefingers173 of the laparoscopeouter sleeve171 will maintain the spacing between the adjacent vertebrae, the distractor tip is being removed from the disc space to prevent dislodgment of the outer sleeve. In a bilateral procedure, the bilateral bores in the disc each contain a distractor tip. In the preferred method, the right left bore remains in place. Thus, thefingers173 of the laparoscope engaged within one of the bilateral locations share the distraction load with adistractor tip169 disposed within the other bilateral location. When the right side is instrumented with a fusion device, as described below, thefingers173 will be within the left bore in the disc and will share the distraction load with the fusion device.

With the distraction tip removed and the disc space supported by thefingers173, the next step in the inventive method is the preparation of the vertebral end plates and disc to provide a site for insertion of a fusion device. The switchingsleeve190 is first removed and, in accordance with one aspect of the invention, areaming sleeve195 is advanced through thelaparoscope170. As shown in FIG. 21, the reamingsleeve195 includesspikes196 that are adapted to penetrate the adjacent vertebral bodies to hold the reaming sleeve in place. One object of the reaming sleeve in this embodiment is to help maintain the position of the laparoscope while the disc material and vertebral end plates are being reamed. This object is of particular importance when the laparoscopeouter sleeve171 does not include theteeth174. In addition, thespikes195 on thereaming sleeve195 will prevent the vertebral bodies from being pushed away or distracted while reaming, since the force generated by the reamer can have a tendency to drive the vertebral bodies apart. This force is particularly present when a tapered fusion device is to be implanted, necessitating cutting conical threads into the vertebra.

In accordance with the invention, anadjustable reamer197 is extended through thereaming sleeve195. Thereamer197 can be of conventional design with a cutting surface configured to evacuate the disc space and prepare the adjacent vertebral bodies to receive a threaded implant. Thereamer197 includes an adjustable depth stop198 disposed adjacent thelaparoscopic port180. Thedepth stop198 contacts theseals182 of the port to prevent introduction of thereamer197 to deeply into the disc space. The depth of reaming necessary, and consequently the position of thedepth stop198, can be determined prior to this reaming step by review of fluoroscopic images.

Thereamer197 is manually operated by way of a T-handle199 to successively remove disc tissue and bone from the adjacent vertebral bodies to provide a prepared bore for the fusion implant. Preferably, several passes will be made with the reamer, after which the outer sleeve will be examined visually and fluoroscopically to verify that it remains fully seated within the disc space. In addition, the reaming should be observed under C-arm imaging to prevent reaming into the spinal canal. Preferably, thedepth stop198 will be set at an initial drilling depth less than the anticipated full depth for implant insertion. For example, for an L5-S1 fusion, a 20 mm deep reamed bore may be prepared for a 26 mm long implant.

After the disc material and vertebral bodies have been reamed by thereamer197, one prepared site is available for insertion of the fusion implant at the right location MR. It is then necessary to prepare the other bilateral location previously marked using the template150 (location ML in FIG.15). In the next steps of the inventive method, thereamer197 is withdrawn as well as thereaming sleeve195. Thelaparoscope170 is then unseated in a controlled manner so that thefingers174 are disengaged from between the vertebrae and withdrawn through the opening of the disc annulus. However, thelaparoscope170, and particularly theouter sleeve171, is not removed from the skin after unseating from the disc space. Instead, the outer sleeve is reoriented over the second bilateral location ML (see FIG.15). Preferably, immediately after theouter sleeve171 is disengaged from the disc annulus, the switchingsleeve190 is extended back through theouter sleeve171 so that thetapered end191 of the sleeve extends beyond thefingers173. The switching sleeve will then protect the soft tissue surrounding the instrumented disc space as theouter sleeve171 is repositioned over the second bilateral location ML.

With thelaparoscope170 oriented over the second location ML and with the switchingsleeve190 contacting the disc annulus, adistractor tip169 attached to adistractor shaft168 is extended through theouter sleeve171. In the preferred technique, the laparoscope is not yet fully seated at this location ML. Thedistractor tip169 is advanced through the bore within the disc and anchored between the adjacent vertebral end plates. Thelaparoscope170, and particularly theouter sleeve171, is reseated within the disc space in the manner described above, namely with thedistraction fingers173 disposed between the vertebral end plates. Once the position of the outer sleeve andfingers173 is confirmed using fluoroscopy, the remaining steps for preparing the vertebral bodies to receive the fusion implant are repeated at the left location ML.

Once the second bore in the disc space has been prepared, the following steps of the technique involve insertion of the implant. In accordance with the present invention, the implant can be a fision cage of the type shown in FIG. 1 which is tapered to restore the normal curvature at the particular vertebral level. In the case of a fusion cage of the type shown in FIG. 1, theimplant driver50 can be used to implant thedevice10. The implant drive50 can be substantially as depicted in FIG.2 and can engage theimplant10 as shown in FIG.3. In accordance with the present technique, theimplant drive50 can be engaged by a T-handle assembly200, as shown in FIG.22. The T-handle assembly200 includes acollet201 which engages the end of theimplant drive50 opposite the grippingtongs54. Theassembly200 also includes T-handle202 which is aligned with the grippingtongs54 so that the surgeon has a visual indication of the orientation of thetongs54 when the implant driver560 is extended through thelaparoscope170.

In accordance with the preferred technique, theimplant drive50 carrying thefusion device10 is inserted through thelaparoscopic port180 and through theouter sleeve171 until theimplant10 contacts the prepared bore within the disc space. At that point, theimplant drive50 can be rotated using the T-handle202 to thread the implant into the prepared bore. Theimplant driver50 can preferably include a plurality of depth markings on thedriver shaft51 beneath thecollet201 to give the surgeon the visual indication of the depth of insertion of theimplant10 into the prepared bore. Once the implant has been screwed in to its predetermined depth, as indicated by the depth markings on theimplant drive shaft51, insertion of the implant should be halted with the T-handle202 parallel to the vertebral end plates. With this orientation of the T-handle202, thetongs54 of theimplant drive50 will be exposed to the disc space, rather than in contact with the vertebral bone. Consequently, then the long slots27 (see FIG. 1) of thefusion device10 will be directly exposed to and in contact with the vertebral bodies.

With afusion device10 implanted within the left location ML, the implant driver is removed from the implant and thelaparoscope170 is unseated from the left bilateral location. Again, thelaparoscope170 is not removed from the skin after unseating, but is simply moved to the next bilateral location MR, preferably with the switchingsleeve190 protecting the surrounding tissue from thedistraction fingers173 of the laparoscope. At this location, the same steps are repeated to implant asecond fusion device10 at this right location.

When each of theimplant devices10 is bilaterally implanted within the disc space, the position of the implants should be confirmed. In some instances, it may be necessary to reposition an implant within the disc space, such as by driving it further into the disc space. In this instance, the drivingattachment120 can be engaged to theimplant drive50 and theattachment120 engaged with the implanteddevice10 to permit additional manipulation of the device.

In switching between the left location RL and the right location MR, it is preferred that theimplant drive50 be fully removed from thelaparoscope170 and the switchingsleeve190 extended through theouter sleeve171. Also, thedistractor tip169 attached to thedistractor shaft168 should then be extended through the switchingsleeve170 and the distractor tip can be used to locate the previous bore at the right location MR. Once thedistractor tip169 is situated within the bore, theouter sleeve171 can be seated at the right most location in the disc space. With theouter sleeve171 properly seated, the distractor shaft can be removed to make way for theimplant drive50 carrying a newimplant fusion device10. Of course, the switching sleeve is removed prior to extending the implant and implant drive through theouter sleeve171.

Once both fusion devices are disposed in their bilateral positions at location ML and MR, an A-P radiograph can be taken to assure proper placement. In addition, where possible, it is preferred that additional bone graft material is packed around the implants in situ to further facilitate fusion.

As discussed above, thefusion device10 includes ahollow opening15 to receive bone growth material. In one specific embodiment, this bone growth material can include autogenous bone harvested from the patient's anterior iliac crest. Autograft bone from other locations, autologous bone, allograft, bone growth substitutes or other bone material capable of promoting or inducing bone ingrowth can be loaded into the implant. In the preferred technique, theinterior15 of eachfusion implant10 is filled prior to insertion of the implant into the disc space.

The facilitate this “pre-loading” of the fusion material, animplant holder210 is provided in accordance with the invention (FIG.23). Thisholder210 includes a base211 that includes a fixedclamp section212 and amovable clamp section215. The fixedclamp section212 includes aflange213 projecting from thebase211. The movable clamp section includes animpactor plate216 that slides within agroove217 formed in thebase211. Theimpactor plate216 is connected by a threadedshaft218 to aknob219. The threaded shaft is rotationally supported by anupstanding flange221 attached tobase211. Theupstanding flange221 includes a threaded bore (not shown) through which the threadedshaft218 extends. As theknob219 is rotated, the shaft rotates within the threaded bore of theflange221 to move theimpactor plate216 forward toward the fixedclamp half212.

In accordance with the present embodiment, a pair ofblocks225 and226 are provided which are disposed adjacent a corresponding one ofclamp sections212 and215. Theblocks225 and227 include implant engagement surfaces226 and228 which are configured to match the outer shape of the implant at itslarge slots27. These blocks, therefore, serve to close off theslots27 as bone growth material is packed into theopening15 of theimplant10. In one specific embodiment, theblocks225 and227 are formed of plastic to effectively seal thelarge openings27 in the sides of theimplant10. Once the bone growth material has been tightly compacted within theimplant device10, theknob219 can be rotated in the opposite direction to release themovable clamp216 from thedevice10.

In accordance with another aspect of the present invention, thelaparoscope170 can be used to implant abone dowel240, as depicted in FIG.24. Thebone dowel240 can be of a variety of configurations, such as an allograft Crock dowel, autograft tricortical or button dowels, manufactured composite dowels or hybrid dowels (e.g., an autogeneous button combined with allograft Crock dowel). While it is preferable that thebone dowel240 be cylindrical, this configuration is not essential to the invention, provided the dowel is configured to pass easily through theouter sleeve171 of the laparoscope.

In accordance with this embodiments, the disc space and adjacent vertebral bodies are prepared as described above (see, FIGS. 13-21 and accompanying text). In the preferred technique for implanting a bone dowel, thereamer197 is used to create a partially cylindrical cut in the vertebral endplates to receive a cylindrical dowel. Alternatively, if a non-cylindrical dowel is used, the endplates can be prepared accordingly. It is understood that the dowel will typically have a uniform outer diameter or width corresponding to the disc space height. Unlike thefusion device10 discussed above the bone dowel is not tapered; however, preparation of the vertebral bodies with the tapereddistraction fingers173 of theouter sleeve171 providing an appropriate angle will allow the implanted bone dowel to retain this angle.

Once the disc space and vertebral endplates have been prepared to receive the dowel, thebone dowel240 is dropped into the laparoscope throughouter sleeve171. Due to the precise fit between the bone dowel and the vertebral endplates, resistance will be experienced during insertion of the dowel. Animpactor245 is provided to drive the dowel into its prepared site. The impactor includes animpactor head246 that is preferably threaded engaged to animpactor shaft247. The head and shaft are sized for a close running fit through theouter sleeve171. Preferably, theimpactor head246 can be provided to be implanted. Also preferably, theimpactor shaft247 will have a smaller diameter so that it can be used with impactor heads and outer sleeves of several diameters.

Theimpactor shaft247 includes a drivingcap248 that can be stricken by a hammer or similar tool to drive the bone dowel into the prepared site in a controlled manner. Preferably, the impactor shaft also includes a series ofdepth markings249 corresponding to the depth of insertion of thebone dowel240 into the disc space. The final position of the dowel can be verified later by A-P radiograph. The second bone dowel can be inserted in a similar manner and additional bone graft placed between the bilateral bone dowels.

The present invention involves instruments and surgical techniques usable at any level of the spine. For simplicity, the above discussion has focused on fusion of the L5-S1 disc space. The dimensions of each of the components of the instruments would be sized appropriately for the specific vertebral level being instrumented. For example, thefusion devices10 may be offered in several sizes, including 12 mm, 14 mm, and 16 mm. Based upon the size of the fusion implant, thetrephine165 can be provided in several sizes, such as trephines to form bores having a diameter of 6 mm, 8 mm or 10 mm.

Thedistractor tips169 are also sized according to the size of the fusion device to be implanted. Preferably, the distractors are smaller than the fusion device. For example, for a 16 mm fusion device, thedistractor tips169 can be either 12 mm or 14 mm. For a 16 mm fusion device, a 16 mm reaming sleeve is provided to accept a 16 mm reamer to prepare a hole of the same diameter within the disc space and vertebral bodies. Smaller reamers and reaming sleeves would be provided for smaller fusion devices. As previously described, theouter sleeve171 of thelaparoscope170 is preferably a 2 mm in diameter to readily accept all of the instruments and sleeves passing therethrough during the several steps of the inventive procedure.

In the surgical techniques described above in relation to FIGS. 13-21, anouter sleeve171 is utilized which incorporatedfingers173 that served to maintain distraction of the intervertebral space. In addition, the prior illustrated technique utilizes a series ofdistractor tips169 that are used to maintain distraction at one side of the disc space while a fusion device is implanted in the other bilateral location. A further embodiment of the present invention provides an improvement to this technique. Specifically, this improvement resides in a distraction mechanism that is centrally disposed between the bilateral fusion device locations. This centralized distraction provides a more uniform distraction across the entire disc space than can be provided by a distractor tip, such astip169, situated at one side or the other of the intervertebral space.

In accordance with the embodiment of the invention shown in FIGS. 25-27, adistractor plug290 is provided that includes anelongated stem291 terminating at one end in a fan-shapedflange292. The stem is sized to be maintained within the disc space. In one specific embodiment, thestem291 has a length of about 22 mm. Theflange292 includes a forward facingbone contacting face293 that is adapted to contact the vertebral bone in a manner disclosed herein. Theelongated stem191 includes opposite inwardly curved or concave walls194. The curved walls194 of thestem191 merge into or are contiguous with opposite curved orconcave edges195 of theflange192. In accordance with the present invention, thesecurved walls294 andcurved edges295 are preferably sized to provide clearance for the outer diameter of various tools and instruments that might be advanced into the intervertebral disc space through an outer sleeve, such as thesleeve171 described above. In a specific embodiment, these contiguous curved walls194 andedges195 are defined at a diameter of between 20 mm-29 mm.

Thedistractor plug290 further includes a lockingsurface297 at the top and bottom portions of theelongated stem291 and intermediate between the oppositecurved walls294. These locking surfaces297 can have a variety of configurations; however, in one specific embodiment, these lockingsurfaces297 includes a series ofridges298 that are adapted to provide a modest grip on the endplates of the adjacent vertebrae that will contact theelongated stem291 of thedistractor plug290. In accordance with the invention, theelongated stem291 has a height between the two lockingsurfaces297 that approximates the distracted height of the disc space to be instrumented. In the case of a threaded fusion device, such as thedevice250, this height of theelongated stem291 will be less than the outer crest diameter of the threads of thefusion device250. In a specific embodiment, the top and bottom locking surfaces297 define an outer diameter of between 10 mm-14 mm.

Thedistractor sleeve290 further includes alower stop face296 that is integral with theflange292 but that is on the opposite side of theelongated stem291 from thebone contacting face293. Theelongated stem291 is hollow with a bore extending along its length, as shown in FIG.26. Thestem291 defines a threadedbore302 at the end adjacent theflange292. The threaded bore merges into and communicates with akeyed bore301 that is at the opposite end of thedistractor plug290. The opposite end of thestem291 of theplug290 forms ablunt nose299 through which the keyed bore301 exits. In the illustrated embodiment, thekeyed bore301 is square in configuration. Alternatively, the keyed bore can have a variety of shapes that permit a keyed interface with a similarly shaped spike extending through thebore301.

In its use, thedistractor plug290 is configured to be pushed into the intervertebral disc space between adjacent vertebrae. Thedistractor plug290 is particularly well suited to providing distraction in a disc space spanning a spondylolisthesis condition. In this condition, one of the vertebrae is anteriorly offset from an adjacent vertebrae. In the condition specifically illustrated in FIG. 28, the superior lower lumbar vertebrae L5 is offset from the inferior sacral vertebra S1. Thus, thedistractor plug290 is advanced anteriorly into the disc space between the lumbar vertebra L5 and sacrum S1.

Theblunt nose299 first contacts the adjacent vertebrae and provides a smooth and steady distraction as the remainder of the plug, namely theelongated stem291, comes in contact with the endplates of the adjacent vertebrae. In order to drive thedistractor plug290 into this disc space, the present invention contemplates aplug driver305. While theplug driver305 can have a variety of configurations, in its simplest form thedriver305 includes a threadedstem306 projecting from anelongated bar307. Ahandle308 is formed at an opposite end of thebar307 to provide a gripping surface to push theplug driver305 toward the instrumented disc space. The threadedstem306 of theplug driver305 is configured to engage the threaded bore302 of thedistractor plug290. Thus, thedistractor plug290 is first threaded onto the end of theplug driver305 and then subsequently advanced anteriorly into the disc space between the adjacent vertebrae.

As a force F is applied to thedistractor plug290 through theplug driver305, theflange292 is advanced toward the lumbar vertebra L5 until thebone contacting face293 is in contact with the vertebra. At this point, further force F applied to thedistractor plug290 not only pushes theelongated stem291 into the intervertebral space, but also pushes the lumbar vertebra L5 into its proper alignment with the sacrum S1.

As thedistractor plug290 is advanced further into the intervertebral space, the upper and lower locking surfaces297, and particularly theridges298, grip the adjacent vertebral endplates to prevent retrograde expulsion of thedistractor plug290. The locking surfaces297 of thedistractor plug290 provide a sufficiently strong engagement between the vertebral endplates to also prevent restoration of the original spondylolisthesis condition. Thedistractor plug290 is pushed further into the intervertebral space until thestop face296 of theflange292 contacts the inferior vertebra, in this case the sacrum S1. It is understood that thisstop face296 can have a variety of configurations depending upon the desired final orientation of the two vertebrae relative to each other. For instance, theflange292 can be wider at thestop face296 than at thebone contacting face292 so that the anterior portion of the displaced vertebra still retains some anterior offset from the anterior portion of the properly positioned vertebra.

It is known that some threaded cages can permit a reduction of a spondylolisthesis condition, provided the condition is only a grade one. Thedistractor plug290, and particularly the lockingsurface297 of thestem291 and theflange292, permit reduction of higher grade spondylolisthesis conditions. The flange and locking surfaces reduce the risk of slippage between the inferior and superior vertebrae as the superior vertebra is reduced.

In an alternative embodiment, adistractor plug310 is provided that does not include a flange, as in the case of thedistractor plug290 shown in FIG.25. Specifically, thedistractor plug310 shown in FIG. 20 includes an opposite curved orconcave sidewall311, ablunt nose312 and opposite lockingsurface313. Each of these features is substantially similar to the features of thedistractor plug290. Likewise, thedistractor plug310 includes astop face314 that is adapted to contact the inferior vertebra during the reduction process. Finally, thedistractor plug310 is hollow and includes a threaded bore (not shown) and an integral keyedbore315.

With this embodiment, the primary reduction force is provided by thedriver316, depicted in FIG.30. This driver includes a threadedstem317 that is adapted to engage the threaded bore (not shown) in thedistractor plug310 of FIG. 29. A drivingflange318 is formed so that the threaded stem projects outward from the drivingflange318. The drivingflange318 includes abone contacting surface319 that at least initially contacts only the end of thedistractor plug310 when thestem317 is threaded into the plug. Once thedriver316 is used to push thedistractor plug310 in place, thebone contacting face319 abuts the displaced vertebra and is used to transmit a force to reduce that vertebra.

As described above, the distractor plugs290 and310 first provide a means for reducing a spondylolisthesis condition. Once the vertebral offset has been reduced, the driving tools can be removed and the distractor plugs290,310 left in position in the intervertebral disc space. At this point, a further feature of the distractor plugs comes into play. Specifically looking, for example, at thedistractor plug290, thehollow stem291, and particularly the keyed bore301 provides an interface for a percutaneous surgical sleeve. In one embodiment, such asleeve320 includes atubular body321 as shown in FIG. 31. Adistraction extension322 is formed at one end of thetubular body321. This distraction extension preferably has a height that is comparable to the height of theelongated stem291 so that the extension can assist in maintaining the distracted height of the intervertebral space.

Substantially 180 degrees opposite from thedistraction extension322 is a locatingspike323. In the specific embodiment, the locatingspike323 integrally extends from the end of theitubular body321 contiguous with the outer wall of the body. This locatingspike323 is configured to extend first through the threadedbore302 and finally through the keyed bore301 of thedistractor plug290. The locatingspike323 preferably has a shape that conforms to the shape of thekeyed bore301. In the specific embodiment, that shape is a square, although other configurations can be utilized that prevent relative rotation between thedistractor plug290 and the locatingspike323. The locating spike is preferably long enough to extend through theentire stem291 without projecting beyond theblunt end299 of the distraction device.

The manner of use of the distractor plug and sleeve combination is shown in FIG.32. In particular, it can be seen that adistractor plug290 is centrally located within the intervertebral disc space. Thedistractor plug290 then serves as a locator to an anchor for thesleeve320. Specifically, the locatingspike323 projects into thedistractor plug290 into keyed engagement with thekeyed bore301. As shown in FIG. 32, thesleeve320 is oriented to the right of the centrally disposeddistractor plug290 so that thedistraction extension322 provides outboard support for the distracted disc space. In this position, thesleeve320 can then be used to perform the drilling and reaming operations previously described particularly in connection with FIG. 21, as well as the step of inserting the fusion device as also described above. Thecurved wall294 andcurved edge295 of theflange292 provide clearance for insertion of the various cylindrical tools and cylindrical fusion device into the intervertebral space.

Once a fusion site has been prepared at the right side of the disc space, thesleeve320 can be retracted, so that the locatingspike323 is pulled out of the keyed bore301 of the distractor unplug290. Thesleeve320 can then be rotated to the position shown in phantom in FIG. 32 with thetubular body321 directed to the left of the intervertebral disc space. The same operations can be performed at this location in the intervertebral space. Using thedistractor plug290 and thesleeve320, the present invention provides a means to maintain midline distraction through the center line of the intervertebral disc space. Moreover, the distractor plug provides a constant fixed pivot point for the various operations involved in implanting an interbody fusion device.

In accordance with another embodiment of the invention, asleeve325 is provided as shown in FIG.33. In this embodiment, thesleeve25 includes atubular body326 that has adistraction extension327 projecting from one side of one end of the sleeve. Unlike thesleeve320, thesleeve325 includes aseparate outrigger spike328 that is fixed to the tubular body by way of anengagement flange329. It is understood that theoutrigger spike328 could be integrally formed with thetubular body326 or connected to the body in some other fashion. Nevertheless, a primary feature of thesleeve325 is that thespike328 is disposed outside the diameter or outer wall of thetubular body326. In this manner, thesleeve325 and its hollow cannula opening can be offset further from the midline of the intervertebral disc space. Thus, interbody fusion devices, such asdevice350, can be disposed farther outboard within that space using thesleeve320.

In a further embodiment, a double-barrel sleeve330 is provided. In this embodiment, twotubular bodies331 and332 are affixed at a joint333. Eachtubular body331,332 includes arespective distractor extension334,335. As with the other sleeve embodiments, thedistractor extensions334,335 have a width that approximates the width of the distractor plug.

In this embodiment, abore336 is formed at the joint333 between the twotubular bodies331,332. A spike, in the form of anelongated rod337, is configured to extend through thebore336. This spike can then engage a distractor plug, such as thedistractor plug310 shown in FIG.34. With this double-barrel sleeve330, there is no need to retract the sleeve, rotated to the bilateral position and re-dispose it within a distractor plug, as in the embodiment of FIG.32. This double-barrel sleeve330 provides an additional distractor extension, so that distraction is achieved not only at the midline location of thedistractor plug310, but also at the outboard positions of thedistractor extensions334,335. Again, the distractor extensions are arranged together with the distractor plug so that various percutaneous operations can be occurring through the double-barrel sleeve of and in the intervertebral disc space.

One problem that faces many interbody fusion devices is the risk of backing out or retrograde expulsion of the device. In the case of push-in implants, the natural compressive forces achieved by the disc annulus in a distracted space can have a tendency to squeeze the fusion devices in a retrograde direction. These same forces, coupled with relative movement between the instrumented vertebrae, can also cause threaded fusion devices to slowly unthread. In accordance with the present invention, one embodiment of a fusion cage is provided that is designed to prevent this counter rotation of the fusion device. Thefusion device250 shown in FIG. 8 includes a pair of bone screws that are threaded into the adjacent vertebrae. These bone screws prevent thefusion device250 from rotating within their prepared bores.

Another approach is presented in FIGS. 35-36. In this approach, bilaterally placed fusion devices are connected laterally across the disc space, thereby preventing each device from rotating. In a first embodiment shown in FIG. 35, a pair offusion devices350 are provided that include ahollow body351 having afirst end352 and asecond end353. As with the fusion devices previously discussed, thedevices350 each include ahollow interior355 and anend wall356. The devices also includeexternal threads358 that are adapted to be threaded into a prepared bore in adjacent vertebrae.

In a deviation from the previously discussed fusion devices, thefusion device350 includes arecess360 formed in theend wall356. Alateral groove361 traverses therecess360 and opens at theflat side walls357 of thedevice350. Each device also includes a threadedbore363 centrally formed at the base of therecess360. When eachfusion device350 is placed bilaterally within an instrumented disc space, the devices are separated by some distance, as depicted in FIG.35. This distance is spanned by aconnector plate365. The connector plate includes anelongate arm366 having mating ends367 formed at the ends of the arm. Each of the mating ends367 defines anouter wall368 that is generally configured to conform to therecesses360 in each of thefusion devices350. Theelongate arm366 is configured to rest within thegroove361 so that theconnector plate365 can span between and interconnect the twofusion devices350.

Theconnector plate365 is provided with aslot369 at each of the mating ends367. This slot is oriented directly above the threaded bore363 in theend wall356 of thefusion device350. A lockingscrew370 having a threadedstem371 is provided that extends through eachslot369 and into the threadedbore363. The lockingscrew370 is then tightened into the bore to clamp theconnector plate365 to each of theinterbody fusion devices350. Thus, the presence of theconnector plate365 when disposed within thegrooves361 of the adjacent fusion devices, prevents eachfusion device350 from rotating when within the patient. The length of theconnector plate365 is dictated by the spacing of thefusion devices350 within the disc space.

In an additional embodiment, aconnector plate375 is shown in FIG.36. The connector plate includes anelongate arm376 with mating ends377, each element of which is similar to the like named elements of theconnector plate365. However, in an alternative configuration, theconnector plate375 includes anintermediate plate379 that preferably projects perpendicularly outward from theelongate arm376. Theintermediate plate379 is generally in the middle of theconnector plate375 and sized to sit between each of thefusion devices350. In one specific embodiment, theintermediate plate379 has a width that is sufficient so that theplate379 is in contact with oneside wall357 of theadjacent devices350.

In the illustrated embodiments, the focus has been on threaded fusion devices. However, it is understood that the present invention has utility in implanting non-threaded fusion devices, threaded and non-threaded spacers, and cylindrical or non-cylindrical devices or plugs.

In a further aspect of this embodiment, theintermediate plate379 is provided with angled screw bores380. In particular, these screw bores are angled so that a bone screw inserted through the bores can be driven upward into the vertebral endplates of the adjacent vertebrae. Preferably, the screw bores are oriented at an angle similar to the angle of the screw bores268 of thefusion device250. Thus, theconnector plate375 provides an additional degree of security to prevent retrograde expulsion of theinterbody fusion device350.

While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.

Claims (18)

What is claimed is:

1. An interbody fusion apparatus for implantation in the disc space between adjacent vertebrae to be fused, comprising:

a hollow body having at least an upper substantially cylindrical portion and a lower substantially cylindrical portion defining an outer diameter greater than the height of the disc space between the adjacent vertebrae, said substantially cylindrical portions each configured to contact a portion of one of the adjacent vertebrae, said body having a first end and an opposite second end and including an end wall at said first end, said end wall defining an upper portion and a lower portion;

a first screw bore defined through said end wall upper portion, said first screw bore defining a first longitudinal axis oriented such that said first longitudinal axis intersects said upper substantially cylindrical portion and a second screw bore defined through said end wall lower portion, said second screw bore defining a second longitudinal axis oriented such that said second longitudinal axis intersects said lower substantially cylindrical portion, the longitudinal axis of said first and second screw bores diverging from each other toward said second end; and

a first bone screw sized to extend through said first screw bore and project outward from said upper substantially cylindrical portion through a first aperture and a second bone screw sized to extend through said second screw bore and project outward from said lower substantially cylindrical portion through a second aperture disposed generally opposite said first aperture, said bone screws configured to threadedly engage the adjacent vertebrae to retain said hollow body within the disc space.

2. The interbody fusion apparatus according toclaim 1, wherein:

said hollow body defines a longitudinal axis and a midline extending between said upper and lower substantially cylindrical portions, said midline intersecting said longitudinal axis, and said upper screw bore and said lower screw bore are disposed along said midline.

3. The interbody fusion apparatus according toclaim 1, wherein

each of said two screw bores includes an enlarged recess at said end wall; and

each of said two bone screws includes an enlarged head sized to be received within said enlarged recess.

4. The interbody fusion apparatus according toclaim 1, wherein said at least two substantially cylindrical portions of said hollow body include external threads configured for threaded engagement with said adjacent vertebrae.

5. The interbody fusion apparatus according toclaim 1, wherein said hollow body is tapered from said first end to said second end.

6. The interbody fusion apparatus according toclaim 1, wherein said hollow body defines two opposite substantially flat walls between said at least two substantially cylindrical portions.

7. The interbody fusion apparatus according toclaim 1, wherein said hollow body defines at least one slot extending through said hollow body and intersecting at least one of said substantially cylindrical portions.

8. The interbody fusion apparatus according toclaim 7, wherein one of said screw bores intersects said at least one slot.

9. The interbody fusion apparatus according toclaim 1, wherein:

said hollow body defines a longitudinal axis and a midline extending between said upper and lower substantially cylindrical portions, said midline intersecting said longitudinal axis, and said upper screw bore and said lower screw bore are disposed along said midline; and

further wherein said end wall defines a pair of elongated slots offset from and substantially parallel to said midline of said end wall.-

10. An interbody fusion apparatus for implantation in the disc space between adjacent vertebrae to be fused, comprising:

a hollow body having at least an upper substantially cylindrical portion and a lower substantially cylindrical portion defining an outer diameter greater than the height of the disc space between the adjacent vertebrae, said substantially cylindrical portions each configured to contact a portion of one of the adjacent vertebrae, said body having a first end and an opposite second end and including an end wall at said first end, said end wall defining an upper portion and a lower portion;

a first screw bore defined through said end wall upper portion, said first screw bore defining a first longitudinal axis oriented such that said first longitudinal axis intersects said upper substantially cylindrical portion and a second screw bore defined through said end wall lower portion, said second screw bore defining a second longitudinal axis oriented such that said second longitudinal axis intersects said lower substantially cylindrical portion, the longitudinal axis of said first and second screw bores diverging from each other toward said second end; and

a first bone screw sized to extend through said first screw bore and project outward from said upper substantially cylindrical portion through a first aperture and a second bone screw sized to extend through said second screw bore and project outward from said lower substantially cylindrical portion through a second aperture, said bone screws configured to threadedly engage the adjacent vertebrae to retain said hollow body within the disc space:

wherein said end wall of said hollow body defines a threaded bore between said two screw bores: and

wherein said apparatus includes a locking screw configured for engagement within said threaded bore, said locking screw having a head sized to contact each of said two bone screws when said bone screws are extended through a respective one of said two screw bores and when said locking screw is engaged in said threaded

11. The interbody fusion apparatus according toclaim 10, wherein

each of said two screw bores includes an enlarged recess at said end wall;

each of said two bone screws includes an enlarged head sized to be received within said enlarged recess; and

said threaded bore includes an enlarged recess sized to receive said enlarged head of said locking screw therein, said enlarged recess of said threaded bore overlapping said enlarged recess of each of said bone screw bores.

12. An interbody fusion apparatus for implantation in the disc space between adjacent vertebrae to be fused, comprising:

a hollow body having an upper substantially cylindrical portion defining a first aperture and a lower substantially cylindrical portion defining a second aperture disposed generally opposite said first aperture, said body having an end wall defining an upper portion and a lower portion;

a first screw bore defined through said end wall upper portion;

a second screw bore defined through said end wall lower portion;

a first bone screw extending through said first screw bore and said first aperture and into threading engagement with one of said adjacent vertebrae: and

a second bone screw extending through said second screw bore and said second aperture and into threading engagement with an opposite one of said adjacent vertebrae.

13. The interbody fusion apparatus according toclaim 12, wherein said end wall defines a midline extending between said upper and lower portions, said upper and lower screw bores disposed along said midline.

14. The interbody fusion apparatus according toclaim 13, wherein said hollow body extends along a longitudinal axis, said midline intersecting said longitudinal axis.

15. The interbody fusion apparatus according toclaim 12, wherein said upper and lower substantially cylindrical portions define an outer diameter greater than the height of the disc space between the adjacent vertebrae.

16. The interbody fusion apparatus according toclaim 12, wherein

said end wall of said hollow body defines a threaded bore between said first and second screw bores; and

wherein the interbody fusion apparatus further comprises a locking screw configured for threading engagement with said threaded bore and into contact with each of said first and second bone screws.

17. The interbody fusion apparatus according toclaim 12, wherein said upper and lower substantially cylindrical portions include external threads configured for threading engagement with said adjacent vertebrae.

18. The interbody fusion apparatus according toclaim 12, wherein said hollow body defines two substantially fiat walls arranged generally opposite one another and extending between said upper and lower substantially cylindrical portions.

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